To better understand the pathophysiology of the chronically overloaded, failing ventricle we propose to monitor the mechanical and geometrical responses of the experimental canine analog. The specific objectives of this research effort are: a) the description of the time course and functional basis of the failure state, and b) the accompanying measurements of the time-dependent responses in volume, mass, shape and stress distribution during both the developmental and regressional (if any, following correction) stages of the lesion. The instrumented, conscious canine preparation with a pressure (aortic banding) or volume (subclavian artery to left atrium or aorto-caval fistula) overloaded heart will be monitored on a long term basis (1-18 months) both at rest and during periods of stress (angiotensin, 0.1-2.5 micro grams/kg/min; dextran infusion; and treadmill exercise). From the measurements of ventricular pressure, aortic root flow, and the internal dimensions of diameter, length and wall thickness, the systolic tension-length and tension-shortening (rate and extent) relationships will be derived. At predetermined intervals the hearts will be excised for in vitro testing. Here a pressure servo system which permits the continuous monitoring and control of ventricular volume and loading respectively will be applied to the instrumented, isolated heart to investigate the mechanical properties of the overloaded, hypertrophied myocardium and accompanying configurational responses in greater detail. Finally, a separate group of animals with time varying periods of overload will have the inciting lesion corrected and the regressional recovery capabilities of mass, volume and function assessed.